Motive vapour

If jet pumps are driven by steam, waste water is generated when the motive steam is condensed. In this condensate, residuals of product from the suction flow can often be found. Even though this waste water flow rate is small and the costs for handling the effluents are similarly small, it should be an aim to reduce the waste water flow as far as possible. When the ejector is driven by a product vapour, this problem can often be avoided. Normally the motive medium condensate can again be evaporated and reused as motive vapour (Figure 4.17). 

Using the calculation methods of one dimensional gas dynamic shows how different motive media behave during the expansion in the motive nozzle. Depending on the expansion ratio ( = motive vapour pressure/suction pressure), the Mach number at the motive nozzle outlet for some vapours is charted in Figure 4.18. It can be seen, that the velocity is in the supersonic range and therefore the corresponding effects (expansion, compression and shock waves) have to be considered. 

In this way the general solution has been obtained to the problem which I originally propounded, namely, the calculation of the maximum work (free energy, chemical affinity, electro-motive force, vapour pressure, etc.) from purely thermal quantities, namely, specific heats, heats of transformation, heats of reaction of all sorts or, expressed in more general terms, whereas before U could be calculated when A was known for all temperatures but not the converse, the latter is now also possible. 

Electro-motive Force.—Helmholtz showed, as early as 1889, that the dissociation of water could be theoretically calculated from the electro-motive force of polarization, but in this particular case the counter E.M.F. of the reversible decomposition of water cannot be directly determined. In other cases, however, the method has proved itself applicable e.g. from the E.M.F. of the hydrogen-chlorine gas cell and the HCl-vapour tension of the acid used, the dissociation of hydrochloric acid can be determined at ordinary temperatures, and then that at very high temperatures obtained with the aid of the molecular heats of the reacting gases, which have been measured by Pier up to very high temperatures (25). 

The electro-motive force of the hydrogen-chlorine gas cell is well known from this the dissociation of hydrochloric acid gas may be derived, knowing the HCl-vapour pressure of the solutions used. With the further assistance of the equilibrium in the Deacon process,... 

Of particular importance is the result of a similar calculation, namely, the derivation of the electro-motive force of the oxy-hydrogen cell from the dissociation of water vapour. Calculation, the principle of which dates back to Helmholtz, led v. Wartenberg and me (1906) to the result... 

Jet pumps are devices for the transfer, compression or mixing of gases, vapours, liquids or solids, in which a gaseous or Uquid medium acts as the motive force. They operate by the conversion of pressure energy into velocity by means of suitable nozzles. They are pumps without moving parts (Figure 4.1). 

A further field of application for product vapour driven ejectors are in processes where the intrusion of water has to be avoided at all costs. In addition, the use of motive media other than steam can also be energy saving. 

The design of product vapour driven jet pumps needs a detailed analysis in order to find the best degree of efficiency. The main fluid dynamic processes in a vapour- or gas-driven ejector are firstly the expansion ofthe motive medium, then the mixing of motive and suction flows and finally the compression of the mixed flow to the required discharge pressure. These processes are influenced by the geometry of the ejector, the properties of the media employed and the prevalent pressures. 

The applicability of a substance to be used as a motive medium in a vapour jet vacuum pump is also considerably influenced by its vapour pressure diagram. It must be considered that the evaporation temperature is always below a possible... 

Figure 4.19 Example for a vapour jet vacuum pump with butanol vapour as motive medium.

The temperature of the available cooling water and the possible condensation pressure can preclude the use of a special motive medium. Also, the variation of the vapour pressure diagram by the addition of other components must be regarded. The example of the twin component system, ethylene glycol/water, makes this point more clearly. Even small parts of water lead to a distinct decrease of the necessary cooling liquid temperature. For example, at 2 mbar and a water content of 1% condensation is possible at 35 °C, but even at 3% water content the condensation temperature has decreased to about 15 C. 

The steam transformers produce a medium pressure motive steam using the steam extracted from the turbine. The produced steam is supplied through the thermal vapour compressor (steam ejector) to the evaporator for desalination. One significant advantage of the MED-TVC process is its ability to use pressure energy of the steam for desalination. The performance summary of the SMART nuclear desalination plant is as follows ... 

Substantial part of my scientific activity was devoted to physicochemical properties of aqueous solutions of citric add and various inoiganic citrates. They included formation of metal-mixed complexes, determinations of solubiUties, vapour pressures of water above citric acid and citrates solutions, densities, melting points, sound velocities and electrical conductances. Unquestionably, the industrial and biological importance of citric acid was the main motivation that more than 25 sdentific papers I pubhshed together with my coworkers on systems with citrate ions. Our results up to 1994,1 summarized in the review entitled Thermodynamic and Transport Properties of Aqueous Solutions of Hydroxycaiboxylic Acids. The current book came as a desire to enlarge the information about citric acid properties presented there, to incorporate some subjects which were entirely omitted (chemistry of citric acid and properties of inorganic citrate solutiorrs) and finally to include our and others new relevant results. 

Ionic liquids (ILs) are probably one of the most studied chemical compounds in the last decade. This is particularly motivated by ILs imique physical-chemical properties that enable their application in a broad range of scientific fields. ILs are comprised entirely by ions and most of them exhibit a negligible vapour paessure, ionic conductivity and a high thermal, chemical and electrochemical stability. (Femicola et al., 2006 Galinski et al., 2006 Lu et al., 2002)... 

The application to be considered is a plant with a compressor drawing vapour from the top of a distillation column and moving this vapour to downstream processing units. The plant also has a considerable amount of waste heat in the form of steam therefore, it is economically worthwhile to use steam turbines as drivers with superheated steam as the motive force. The schematic of the example plant is shown in Figure 7.30. 

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